1. Field of the Invention
The present invention relates to medical devices; more particularly, this invention relates to catheters and in particular agent delivery catheters.
2. Background of the Invention
Steerable catheters have been commonly used in applications such as mapping (e.g., cardiac mapping), drug delivery (e.g., intramyocardial drug delivery), and ablation, (e.g., arrhythmia ablation).
A steerable catheter has a deflectable, flexible distal section and a stiffer proximal shaft. Locating a tip of a steerable catheter in three-dimensional space during a medical procedure involves three distinct modes of operation for the catheter: translational catheter movement along the shaft direction, deflection of the flexible distal section, and turning of the catheter shaft to direct the deflection toward a target therapy site. A tendon wire is included to control the deflection of the distal section. This tendon wire is located inside of a sheath running along and within the catheter shaft with its distal end attached near the distal tip of the catheter. A pulling mechanism is included within the proximal catheter handle, which is coupled to the proximal end of the catheter shaft. The pulling mechanism controls the tendon wire to deflect the distal section of the catheter shaft. Radially, the tendon wire is located off-center of the catheter shaft center to create a moment toward the intended deflection side in the catheter distal deflectable section. When the tendon wire is pulled, the catheter deflects toward the radial direction to which the tendon wire is located. The deflection section is typically made to be much more flexible than the rest of the catheter shaft. When the tendon wire is pulled in tension, the catheter shaft wants to “curl up.” The distal section is the most flexible section of the catheter shaft and thus it deflects when the tendon wire is pulled. To direct the deflected section toward the target site, an operator turns the catheter shaft on the proximal end. The deflection section responds to the torque in a fashion that is governed by the way the catheter is constructed.
One problem commonly occurring in the working of this kind of catheter is that the catheter whips when rotated from the proximal end of the shaft. Whipping is caused by the resistance of the catheter to turn away from its preferred orientation. This whipping problem gets further magnified when the catheter distal section is deflected and/or when the catheter is resident in tortuous vasculature.
There is a need to improve upon catheter shaft design so that it can exhibit more beneficial torque response without significant whipping, i.e., controlled whipping. This will provide the physician with more ability to aim the catheter tip, which can lead to improved delivery accuracy and treatment outcome.
Agent delivery catheters have been proposed for treating conditions relating to congestive heart failure. This disease progresses cyclically, the cause being overcompensation of the heart muscle to make up for the loss of function from infracted myocardium. As the heart continues to overcompensate, more tissue becomes infracted, and the heart grows in size until the anatomical valve structures can no longer operate as intended. The resulting complications become extremely serious. Existing methods for treating congestive heart failure include the removal of infarct tissue and the constraint of the heart muscle.
Another approach for treating infarct myocardial tissue is the implantation of cells, such as mesenchymal stem cells, skeletal myoblasts, bone marrow mononuclear cells, etc., which will facilitate the revitalization of the infracted heart tissue. Hereafter, these types of materials, as well as solutions containing them, will be referred to as therapeutic agents.
Delivery of the therapeutic agents has generally required that a needle puncture the myocardial tissue prior to delivering a bolus of therapeutic agent through a needle lumen into the tissue. Multiple punctures may be required, and each puncture causes some amount of tissue trauma due to the mechanical stress that the penetration creates.
There is a need to provide an active means of delivering drug into a vessel wall while reducing the mechanical trauma that needles can introduce.
Deflection of the catheter shaft, particularly the distal portions, creates internal strains on components that are necessarily made flexible to enable the catheter to be navigated through tortuous anatomy and directed to various locations within a vessel for delivery of a therapeutic substance. The method used for steerable catheter, as discussed briefly above, involves both a transverse loading and axial loading on components. One consequence of this deformation is a loss in control over an injection needle. For effective treatment, a physician needs to know the exact position of a needle relative to a target tissue. If the needle position relative to the tip of the catheter has changed, due to tension applied by a steering tendon, then it may be difficult to accurately locate the piercing tip of the needle relative to the tissue wall. In view of these shortcomings, there is a need to improve the needle accuracy and repeatability (or NEAR) of a needle injection device, such that the extension of the needle from the tip of the catheter, as a result of an axial translation of the needle at the proximal end of the catheter is accurate and repeatable.
During delivery and use of a steerable agent delivery catheter, the tip of the catheter may experience external forces that can dislodge the tip from the catheter, leading to medical complications. If a tip of a catheter were to become dislodged within a patient, it could potentially enter the patient vasculature, which may lead to severe medical complications. To avoid this occurrence, there is a need for better securement of a catheter tip to the distal end. A typical manufacturing process that bonds a distal tip to the catheter body or stiffening member requires the administration of an adhesive to the parts. Adhesive processes may have variations that are difficult to control and difficult to validate. Therefore, a securement means that is more reliable, i.e., will resist dislodgement of the tip during use, and provides more straight-forward manufacturing process and quality control is needed.